Mesoscale simulations with MRAMS of atmospheric response to chaos formation

Do Hesperian plateau channel networks record local or global climate conditions?

Edwin Kite (UC Berkeley) Collaborators: Scot Rafkin & Tim Michaels (SwRI) Michael Manga (UC Berkeley)

Outline Channels on the Valles Marineris plateau:

formed by chaos storms? The Mars Regional Atmospheric Modeling

System (MRAMS) Boundary conditions Results

Plateau channel networks• Remarkably late in Martian

history– Overlie Late Hesperian lavas– Main epoch of valley network

formation tightly constrained to Late Noachian – Early Hesperian (Fassett & Head, JGR, 2008)

• Associated with opal, ‘jarosite’ bearing light-toned layered deposits

• Sometimes inverted relief• No HiRISE-resolved clasts• Multiple periods of flow; in

places, flow direction changed over time

• Strong evidence for precipitation, not groundwater– Drainage density, branching order,

tributaries extend to near ridges– Phase (rain vs. snow) not clear

• Local, regional or global climate change?

Williams et al., LPSC, 2005Milliken et al., GRL, 2008; Weitz et al., GRL, 2008

Bishop et al., JGR, 2009; Weitz et al., Icarus, in press

MO

C N

A R

08-0

2129

2

1.5km

Localized, chaos-induced precipitation?

MEGAOUTFLO hypothesis: Vapor release to atmosphere by chaos outflows produces transient global greenhouse.

- Baker et al., Nature, 1991; Baker, Nature, 2001.

But hydrologic models suggest individual chaos-forming events were small.

- Andrews-Hanna & Phillips, JGR, 2007 Harrison & Grimm, JGR, 2008.

Therefore, a localized response to chaos formation might be expected – mesoscale, not global.

- e.g., Mangold et al., 2008.

Test

loca

tion:

Juve

ntae

Flooding level

Forced by present-day (Ames) GCMPressure 2x present-dayFixed lake surface temperature and elevationSurface albedo -> 0.75 when water ice landsFlooded to -1000m, just below spillway elevationGrid resolution 8.33 km (finest grid)approx. 40 CPU-days 50km

-1000 mcontour

spillway

Area of inverted channels Area of LLD

from Weitz et al., Icarus, in press

crater

OUTFLOW

CHANNEL

Hypothesis test with MRAMS

Mars Regional Atmospheric Modeling System (Rafkin et al., Icarus, 2001)

Non-hydrostatic mesoscale modelUsed in landing-site downselect for MER, PHX, MSLBoundary conditions supplied by GCMNested grids (8 km resolution on finest grid)Water vapor treated as a trace gas CARMA-derived ice and dust aerosol microphysics

Monin-Obukhov surface flux parameterizationModified to include ITS-90 saturation vapor pressure

Hypothesis: Given a chaos region filled to spillway with water at 5 deg C,

(1)Precipitation location matches mapped light-toned layered deposits(2)Precipitation magnitude can move sediment through mapped inverted channels.

Atmospheric response

460 km

42 k

m

FloodedJuventae Chasmafloor

Observed layereddeposits

X-Zsection

ALL RESULTSARE PRELIMINARY

peak ~ 1.4%

MGCM, 1.25 days water release:Ls = 270°, PCO2 = 2 x PAL

Steady state zone of precipitation has been established1.25 days

640 km

Rates in inverted-channel area are steady

Precipitation

SnowPeak value:3.96 g/cm^2 in 1.25 daysIn 1 Earth year, 1200 g/cm^2

Strong precip on chasm walls expected ALL RESULTSARE PRELIMINARY

Mean ice precip rate in mm/hr

W-directed winds + promontory effect + rapid rainout

Area of channels Area of LLD

from Weitz et al., Icarus, in press

Precipitation is highly localized

At 2 x PAL CO2, conditions on the plateau permit melting of precipitated water ice

Max. air temp from control run Max. surface temp from control run (K)

With albedo 0.7, temperatures are always less than 273.15K.

Modeled precipitation rates are sufficient to move gravel through mapped channels

Perron et al., JGR, 2006

PS

P_0

0372

4_17

55

dd =1.33 km-1

Outstanding issues / Next steps1) Physics:

Sensitivity tests show a trend of reduced vapor release with reduced grid spacing in z; The model has an inadequately-resolved water vapor concentration boundary layer.

Treat water vapor as a bulk constituent of the atmosphere - Pressure & virtual temperature effects of H2Ov (pressure source; different molecular mass)

Self-consistent lake thermodynamicsWind-dependent lake surface roughness parameterization from Shieh et al., 1979New locations: Echus & Ganges

2) Geology:

Are modelled precipitation rates sufficient to initiate observed channel network?

Look for additional inverted channels/layered deposits around chaos rims.

Search for opal or jarosite bearing deposits on the plateau far from candidate paleolakes(would disprove the localized-precipitation hypothesis).

SummaryAtmospheric response is “hurricane-like”

- Water vapor mass ratio reaches 0.3 (>> trace)

Juventae channels correspond to a local maximum in water-ice precipitation

- No channels in available (CTX) images of the south chasm wall

Water-ice precipitation is highly localized- Inverted channels on the Valles Marineris plateau far from

paleolakes would disprove the localized-precipitation hypothesis

Chaos storms can mobilize sand and perhaps gravel but not boulders.

- Detection of HiRISE-resolvable clasts would be a severe challenge for the localized-precipitation hypothesis

Backup slides

What is the range of acceptable lake surface temperatures?

• Vapor -> atm. will be small unless freezing of top of lake can be delayed -- 4.18 K for fresh water

• In model, evaporative cooling ~ 2 KW/m2 -- Sensible heat cooling < 1% of total cooling

• Heat sources– fracturing mixes reservoirs

that are isolated by low permeability

– Shear heating– Clathrate decomposition (?)– Most important: volcanic

heating – Warmest (deepest) water will

arrive last (Andrews-Hanna & Phillips, 2007).

McKenzie & Nimmo, Nature, 1999